The present invention relates to a Colpitts type quartz crystal oscillator.
Quartz crystal oscillators are popular in the art due to their extremely good frequency stability. However, a problem has heretofore remained unsolved regarding stability of oscillation. The equivalent resistance of the crystal of such oscillators is typically between 50 and 100 ohms when the driving excitation, or the amplitude of the oscillating voltage across the crystal, is below a predetermined value and drops down to about 10 ohms when the driving excitation exceeds the predetermined value. With the low driving excitation it is impossible in some cases to get oscillation to occur. In cases where oscillation does occur with low driving excitation, the stability of oscillation is quite poor.
Increasing the driving excitation above the predetermined value where the equivalent resistance drops will ensure that stable oscillation will occur. However, the intensity of oscillation is so high that second, third and higher order harmonics are generated and the oscillator signal may be undesirably coupled to other sections of the electrical apparatus in which the oscillator is incorporated.